Guidance systems for guiding a catheter through tissue within a body are described. In one form, the system is implemented in connection with a catheter which includes a catheter body having optic fibers extending between a first end and a second end thereof. The guidance system is coupled to the catheter body and includes a first optic fiber, a second optic fiber, and a detecting element. The first optic fiber includes a first end and a second end, and is coupled to the catheter body so that the first optic fiber second end is adjacent the catheter second end. The second optic fiber also includes a first end and a second end, and a reference mirror is positioned adjacent the second optic fiber second end. The first optic fiber first end is communicatively coupled to the detecting element and the second optic fiber first end is communicatively coupled to the detecting element. The detecting element is configured to determine interference between a light beam propagating through the first optic fiber and a light beam propagating through the second optic fiber.